The study on the variation of runoff not only helps to master the evolvement rule of runoff under the background of change climate, but also causes the results of hydrological analysis, hydrological simulation and hydrological calculation to be more accuracy.The object of study in this paper is the Wei River Basin.The heuristic segmentation algorithm and approximate entropy theory are employed to detect the mutation points of the annual runoff in the Wei River basin.The diagnosis results suggest:there are two mutation points, 1972 and 1994, in the basin above Linjiacun; there are no variation points in the basin above Zhangjiashan; there are two change points, 1970 and 1994, in the Wei River Basin as a whole.Furthermore, the attribution analysis on the variation of runoff indicates that the variation of runoff in this basin is caused by the mutual effects of climate changes (the El Nino of 1972 and the ENSO of 1994 events) and human activities (the construction of water conservancy project, the changes in underlying surface and excessive exploitation of groundwater and surface water).